Aching Foot Makes OA-Related Knee Pain Worse

Clinicians should consider evaluating the foot and ankle of osteoarthritis patients

Action Points

Note that this observational study found that, among those with knee osteoarthritis, concomitant foot pain was associated with more severe symptomatology.

Be aware that it remains unclear if the mechanism of foot pain is due to excessive pronation to compensate for the knee pain or other factors.

Foot pain, which may also include ankle pain, affects about a quarter of patients suffering knee osteoarthritis (OA), with such pain exacerbating knee OA-related pain, symptom severity, and physical function, a new study has shown.

"This finding highlights the fact that clinicians should consider evaluating the foot and ankle in people with knee OA and provide interventions for foot pain, if present," wrote the authors, led by Kade L. Paterson, PhD, Centre for Health, Exercise and Sports Medicine, School of Health Sciences, University of Melbourne, Australia.

The results, published in Arthritis Care and Research, also suggest that the laterality of foot pain is important in patients with knee OA.

With international guidelines now recommending that clinicians identify and address different clinical OA phenotypes, a greater understanding of the clinical presentation of patients with concurrent knee OA and foot pain is needed, according to the authors. To date, no study has explained the relationship between foot pain and knee OA-specific symptoms or function, they said.

For this new study, researchers used the publicly accessible database of the Osteoarthritis Initiative (OAI), a prospective multicenter cohort study of 4,796 people ages 45-79 years. They used only data on patients who had experienced knee symptoms such as pain, aching, or stiffness, in and around the knee on most days of the month for at least a month in the past year, as well as radiographic evidence of knee OA.

To assess clinical symptoms, researchers used the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) as well as the Short Form 12 (SF-12) Health Survey and the Center for Epidemiological Studies Depression (CES-D) Scale. For physical function assessments, they used tests of commonly performed daily physical activities, including the 20-meter walk test (WT) measured in meters per second (m/s), and repeatedly standing up from a chair.

They selected the most painful knee as the index knee.

The study, which included 1,255 patients, found that 25.3% (n=317) reported pain in one or both feet. Patients with concurrent foot pain and knee OA were significantly more likely to be younger (P=0.025) and female (P<0.001) and to have a higher body mass index (BMI) (P<0.001) than subjects with no foot pain. More of these patients also had a Kellgren/Lawrence (K/L) grade of 3 and fewer had a K/L grade of 4.

Bilateral pain was the most prevalent type of foot pain (54.9%) and contralateral foot pain the least prevalent (17.7%). Patients with knee OA and bilateral foot pain were significantly more likely to be women and to have a higher BMI, with more having a K/L grade of 3 and fewer a K/L grade of 4.

After controlling for age, sex, BMI, K/L grade, and comorbidities, patients with foot pain performed significantly worse on the CES-D (P=0.007), the SF-12 mental (P=0.017) and physical (P<0.001) component scales, the WOMAC subscales of pain (P<0.001), stiffness (P=0.003), function (P<0.001), and total score (P<0.001), as well as the 20-meter WT (P=0.024), compared with those with no foot pain.

"The between-group differences of 2 points (ipsilateral and bilateral foot pain versus no foot pain) on the WOMAC pain subscale and of 0.06 m/s (foot pain versus no foot pain) and 0.08 m/s (ipsilateral versus no foot pain) on the 20-meter WT, exceed minimal clinically important difference values, suggesting these changes are clinically meaningful," wrote the authors.

This is important, they added, given that people with symptomatic knee OA already experience worse health outcomes and functional disability and concurrent foot pain may further compound these existing deficits.

There were no differences between patients with contralateral foot pain and those without foot pain.

Foot pain may be due to excessive pronation or other biomechanical factors. Such pronation -- and subsequent pain -- could be a compensatory response to OA-related knee pain. Alternatively, both foot and knee pain may be related to the presence of varus knee malalignment, said the authors.

The authors noted that although foot pain adversely affected knee OA symptoms and physical function, the study did not determine if foot pain preceded knee OA, occurred simultaneously with it, or developed after knee OA.

A limitation of the study was that it excluded patients with comorbid conditions that might affect the outcomes of the broader OAI study, possibly resulting in some bias in the sample. Researchers also didn't examine foot pain prevalence according to the knee joint compartment affected by OA.

The authors of this article are not part of the Osteoarthritis Initiative investigative team.

Hinman has received royalties from the sales of an educational osteoarthritis DVD and the Gel Melbourne OA shoe (Asics).

Hunter has received royalties from the sale of a patellofemoral brace (DJO).

Bennell has received consultant fees (less than $10,000) from Physitrack and has received royalties from the sales of an educational osteoarthritis DVD and the Gel Melbourne OA shoe (Asics).

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